1. Technical Field
The present invention relates to a liquid ejecting apparatus and a head unit.
2. Related Art
As an ink jet printer which prints an image or a document by ejecting ink, a printer in which a piezoelectric element is used has been known. The piezoelectric elements are provided corresponding to respective plurality of nozzles in a head unit, and form dots when ink (liquid) of a predetermined amount is ejected from the nozzle at a predetermined timing, by being respectively driven according to a driving signal. Since the piezoelectric element is a capacitive load such as a capacitor in an electrical view, it is necessary to supply sufficient currents in order to operate the piezoelectric element in each nozzle.
For this reason, it is a configuration in which a piezoelectric element is driven, by amplifying a source signal using an amplifying circuit, and supplying the signal to a head unit as a driving signal. For the amplifying circuit, there is a method in which a source signal before being amplified is subjected to current amplification using class AB amplification, or the like; however, since energy efficiency is not good, class D amplification has been proposed in recent years (refer to JP-A-2010-114711). In the class D amplification, plainly speaking, an input signal is amplified by performing pulse width modulation or pulse density modulation with respect to a source signal, switching a high side transistor and a low side transistor which are inserted in series between power supply voltages according to the modulated signal, and by demodulating an amplified-modulated signal which is obtained by performing switching, using a low pass filter (demodulator) which includes an inductor (coil) and a capacitor.
Meanwhile, in order to cause a piezoelectric element to eject ink using a driving signal which is amplified using class D amplification, it is necessary to increase a frequency of a modulated signal to some extent. However, when switching the high side transistor and the low side transistor according to a modulated signal with a frequency which is relatively high, there is a problem in that operations thereof become unstable due to an influence of noise, or the like.